DEVELOPMENT OF PLANTS 



285 



in the stem in a circle and provided with a cambium, so that there 

 is a striking resemblance to the dicotyledonous stem with its pith, 



Fig. 215. The two common genera of the Ophioglossales : A, the adder- 

 tongue fern, Ophioglossum, with single leaf ensheathing the short stem 

 and producing a spore-bearing spike. B, section of the spike— sp, the 

 spore-forming cells arranged in groups or sporangia. The spores are 

 exposed by the breaking apart of the cells between the dark lines. C, 

 stoma from epidermis of spike. D, the grape fern, Botrychium. The leaf 

 is much divided and also forms a branched spore-bearing organ. E, two 

 sporangia, showing the manner of opening for discharge of spores. 



ring of xylem, cambium and phloem, medullary rays, cortex, 

 cork, etc. (Fig. 216). 



The spores are borne in peculiar modified outgrowths of the 

 leaves that assume a cylindrical shape in Ophioglossum and be- 

 come more or less branched in the species of the Botrychium 

 (Fig. 215). The structure of these organs presents many fea- 

 tures that recall the sporophyte of Authoceros (Figs. 215, B ; 

 199). The outer portion of the cylinder consists of chlorophyll- 

 bearing" cells which communicate with stomata in some of the 



